1. Field of the Invention
The present invention relates to a wireless apparatus.
2. Description of the Related Art
Among techniques for reducing power consumption of a wireless LAN base station (access point), there is a technique of reducing the power consumption that is necessary for sending notification signals by suspending beacon transmissions while there is no terminal being in a state that it can communicate with the base station (see JP-A-2003-348104, for instance).
In general, wireless LAN base stations perform beacon transmissions at a constant cycle (e.g., 100 ms). During periods other than the periods of beacon transmissions, wireless LAN base stations perform a standby receiving operation in preparation for reception of a wireless signal.
In such a base station, whereas beacon transmission periods are hundreds of microseconds, standby reception periods are 90 ms or more. Therefore, even if beacon transmissions are suspended to reduce the power consumption of the base station, its power consumption reducing effect is small.
Specific examples of numerical values will be shown below. It is assumed that the power consumption of a signal processor and an analog processor of a base station is 785 mW during beacon transmissions, 230 mW during standby receiving operations, and 230 μW in a sleep mode.
First, where the base station performs beacon transmissions of 100 bytes at a rate of 6 Mbps at a cycle of 100 ms, an average power consumption is calculated as (785 mW×0.133 ms+230 mW×99.867 ms)/100 ms=230.73 mW. In this equation, 0.133 ms is a calculation result of 800 bits/6 Mbps.
On the other hand, when the base station suspends beacon transmissions, an average power consumption is calculated as 230 mW×100 ms/100 ms=230 mW.
That is, even if the technique disclosed in JP-A-2003-348104 is applied to the above base station, the reduction in power consumption is as small as 0.73 mW.
In the technique disclosed in JP-A-2003-348104, the power consumption that is necessary for standby receiving operations of a base station cannot be reduced sufficiently.
On the other hand, suspending standby receiving operations as well as beacon transmissions while there is no terminal being in a state that it can communicate with a base station may prevent the base station from receiving even such wireless signals as a connection request and an authentication request from a terminal. In this case, terminals cannot start a communication with the base station; users cannot use their terminals while the base station is suspending standby operations. The convenience of the users is thus lowered.
Particularly in the wireless LAN, according to Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA), while a wireless channel is not being used by another terminal (in an idle state), a wireless signal is transmitted from a terminal on that wireless channel. Therefore, a base station cannot know in advance when the terminal will send a connection request or an authentication request.
This problem is specific to the wireless LAN that employs CSMA/CA. That is, such schemes as TDMA in which a timing of a wireless signal transmission from a terminal can be transmitted in advance are free of this problem.